Liquid bath arrangement



Nov. l2, 1957 J. A.. LAWLER LIQUID BATH ARRANGEMENT 5 Sheets-Sheet l Filed DSC. 5, 1955 Nov. 12, 1957 1. A. LAWLER LIQUID BATH ARRANGEMENT 5 Sheets-Sheet 2 Filed DSC. 5, 1955 Nov. 12, 1957 J. A.'LAWLER 2,813,189

LIQUID BATH ARRANGEMENT Filed Dec. 5, 1955 5 Shets-Sheet 3 MVA;

5 ySheets-Sheet 4 .JY A. LAWLER LIQUID BATH ARRANGEMENT Nov. 12, 1957 Filed Deo. 5 1955 Nov. 12, 1957 J. A. L AwLER LIQUID BATH ARRANGEMENT 'sheets-sheec 5 Filed Dec. 5 1955 LIQUID BATH ARRANGEMENT periods of time and provides a bath having uniform tem- Joseph Andrew Lawler, Chicago, l1l., assignor to Blue M Electric Company, Blue Island, Ill., a corporation of `Illinois `Application December 5, 1955i, SerialNo. 550,987

21 Claims. (Cl. 219-,38)

The invention relates to a liquid bath arrangement and aV control associated therewith, and particularly to an arrangement that will provide superior results including accurate bath temperature control and novel liquid agitation affording uniform temperature conditions throughout the bath.

In many industrial and commercial applications that require liquid baths it has been found that the baths heretofore used did not offer the accurate temperature control that is required and desired in these modern inst allations. For example, hospitals and scientific laboratories that use liquid baths for heating and storage of specimens, have found difficulties in specimen maintenance due to a variation in bath temperature over a period of time and in many instances a temperature gradient or difference within the bath itself at any given instant of time. Historically, liquid baths of the type here under consideration, provide a container with heating or cooling means adjacent the bottom of the container to heator cool the bath liquid. It was `discovered that baths of thisnature had a temperature gradient within the bath itself, that is, the temperature of the liquid at any instant of time varied between spaced points within the bath. It was found that the natural convection resulting from the application or removal of heat from one portion of the bath did not provide a uniform temperature throughout the bath. Accordingly, prior art efforts were directed to mechanical Vstirring means to induce an artificial circulation of the liquid in the bath in an effort to eliminate the temperature gradient. These devices usually consisted of small fractional horsepower motors having adriven shaft with a propeller arrangement thereon, the latter being inserted into the bath and rotated to set up the mechanical circulation. On larger baths, a plurality of such devices were employed at spaced points in the tank. While these devices offered an improved temperature control as against earlier arrangements, they still proved unsatisfactory in many applications in that each propeller tended only to circulate immediately adjacent or within the vortex liquid and consequently temperature gradients were still found. Further, the provision of severalpropeller devices on a single bath interfered with the bath work area and the storage of specimens in the bath and still failed to provide uniform circulation of the liquid. Additionally, it has been found that the propeller devices heretofore used sometimes caused breakage of specimen containers when accidental contact therebetween occurred.

The problem, therefore, consisted of providing a liquid bath of the type hereunder consideration that would aord accurate temperature control both from the standpoint of extended periods of time and an even temperature throughout the bath itself. The long felt need for an arrangement of this type has been satised by the device herein disclosed.

Accordingly, it is a general object of the invention to provide anY arrangement of the type described, which accurately controls the bath temperature over extended constructed of a non-magnetic material.

perature throughout.

It is a specific object of the invention to provide a bath arrangement having a novel liquid agitating arrangement which will provide gentle and complete circulationV of the liquid within the bath and throughout the entire volume of the bath.

It is a further specific object of the invention to provide an automatically movable plate arrangement to induce and maintain mentioned circulation.

It is yet another object of the invention to provide an electrical control arrangement which induces plate motion by interrupted magnetic action and which provides accurate bath temperature control by means of a novel electrical circuit which controls the application of heat to the bath.

These and other objects of the invention will become apparent in the course ofthe following description and' from an examination of the concerned drawings, wherein: Figure l is a partially fragmentary, perspective view illustrating the invention applied to a bath arrangement.

Figure 1A is a plan view, which illustrates the invention as applied to a liquid bath,

Figure 2 is a partially fragmentary, sectional view taken along line 2-2 of Figure 1A, Y

Figure 3 is a partially fragmentary end elevational view taken from the right of Figure 2,

Figure 4 is a partially fragmentary plan view of the novel temperature control switch employed in the bath,

Figure 5 is a side elevational view, partially in section, of the structure shown in Figure 4,

Figure 6 is a schematic diagram showing the electrical circuit employed in the invention,

Figure 7 is an elevational view illustrating an alternate embodiment of the invention, and

Figure 8 is a top view of the structure shown in Figure 7.

Describing the invention in detail, and directing atten tion to Figure 1 it will be seen that the bath comprises atank, indicated generally at 2, said tank being preferably The tank 2 denes an internal bath compartment 4, said compartment 4Y having a plurality of heater tubes 6 extending longitudinally therein adjacent the bottom of the compartment 4. Immediately above the tubes 6 a false bottom 5 of open meshed construction is located to serve as a support for specimen containers (not shown) that may be placed in the tank. The bottom of the compartment 4 is defined by a horizontal wall 8 located below and in spaced relation to the heater tubes 6. A pair of guide pins 10, 10 (Figure 2) are located at opposite ends of the compartment 4 and secured to the horizontal wall 8 and projects upwardly therefrom.

A movable base plate 12 is positioned in the compartment 4 and is preferably substantially coextensive with the horizontal cross-sectional area of said compartment. The plate 12 may be provided with apertures to receive the pins 10, 10 and cooperate therewith to guide the plate during vertical movement thereof. Other conventional guiding means could be employed if desired. The base plate 12 is located below the heater tubes 6, as is best seen in Figure 3, and is supported in spaced relation to the wall 8 by a pair of longitudinally extending leaf springs 14, which in turn are centrally secured to the underside of the plate 12 adjacent'the opposite long edges thereof. In the preferred embodiment, the plate 12 is non-flexible, that is, it is provided with longitudinally upwardly ex# tending lips 16, 16 and a centrally located, upwardly offset boss 18 whichv provides the plate with the desired rigidity. It will be understood that the plate 12, like the Patented Nov. 12, 1957y thereto and extending transversely thereof, Ysaid plate 20 being formed of a magnetic material. However, it will be understood that the entire'plate 12 may be formed of a magnetic material. y v

Below the tank 2 a housing 22 is provided, said housing extending downwardly in depending relation to the horizontal wall 8. A conventional electromagnet arrange,- ment 24y is located in the housing 22 and extends upwardly into the horizontal wall 8. The magnet is preferably located below the attraction plate 20 andv centrallyof the plate 12 as seen in top plan view. For reasons of quiet and ecient operation, a D. C. electromagnet is Veinlployed inthe preferred embodiment. It be also understood that the walls of the tank 2 are appropriately insulated as at 26. Y

Considering Figures lArand 2 it will be seen that one end of the tank 2 is provided with a chamber 30 receivingV the projecting ends 32 of th'e heater tubes' 6'. A conventional resistor type heat element 34, 34 (Figure 6) is positioned within each heater tube 6 and is provided withelect-rical connections 36 mounted on the projecting ends 32. The chamber 3G houseswthel switches, wiring" andv the like which provide the electrical control f'or both the heating elements 34Kand the electromagnet 24. 'Inasmuch'asf the physical construction of the control devices'ar'e notper separt of the invention` they have not generally been shown in detail, but can readily be Vunderstoodi-byreferring tol the schematic electricalv diagram shown in Figure 6. f A

Directing attention to Figure 6, it will b'e seen that the electrical control circuit comprisesV a power source 40, which may be' a standard llO volt' A. line or in certain 'applications a 220 Yvolt source maybe employed. A main switch 42 isV provided to connect the circuit tothe line. Uponclosing ofthe switch 42 power .is supplied through line 44 to one side of the relay 46 through line 48. The power on condition is indicated by warning light 43. It will be seen that the relay 46 controls a switch 5,0 which establishes a circuit 52 through the heating elements 34. A conventionalcinternal multiple position switch 54, is arranged to control the `power. supply to the elements 34 in a plurality of selectable arrangements, that is, the heating elements 34 may'berarranged in series, parallel or one of Ythe elements may-be disconnected from the circuit'. While only two heatingelements 34 are here illustrated it will be understood that many variations both in number and arrangement of heating elements may be employed depending on the particular application of the herein disclosed invention, such Variation being well withinthe scope of one skilled in the art. The purpose of theV switch 54 is to allow the` bath operator to properly select the power input to theV bath consistent with the particular bathl use, and to economically control the power supplied toY the bath. It will be understood that the action-"of the relay in circuit 48 is controlled by a switching unit 56, said switching unit being illustrated in detail in Figures 4 and 5 and hereinafter more fully explained. Suflce it now to say that the unit 56 comprises a pair of switches 58 andV 60 each of which is available to complete the circuit 48 depending on the position of the selector switch 62. The particular switch controlling the circuit 48Vwill act in response to temperature change of the bath as reported by the sensing bulb 64, which is normally positioned Within the liquid bath itself (Figures 1A and 2). Asy the temperature of the bath begins to uctuate, the bulb 64 senses the change and completes the circuit 48 through'one of the switches 58 or 60. This energizes the relay `46, closing the switch 50 whereby power is supplied to the selected heating elements 34. An indicator lamp 66 may be provided to announce the energizing of the elements 34'.

vAs earlier noted, a D. C. electromagnet 24 is energized to set up a magnetic' e'ld which attracts the magnetic attraction plate 20 secured to the plate 12. Upon ener- .asiarsc l Ygizing of the magnet 24 the plate 12 is urged to move to the bottom of the compartment 4. To accomplish the desired electrical control of the magnet 24, there is provided a circuit 68, said circuit being energized through the normally closed switch 70. In view of the fact that the preferred embodiment uses a D. C. magnet, the circuit 68 to the magnet 24 is provided with a conventional parallel rectifying arrangement 72. A condenser 174 is arranged in parallel with the electromagnet 24 to smooth out the pulsations to the magnet and provide a.

substantially constant direct current tlow thereto. A current limiting resistor and fuse arrangement 76 is provided in the circuit 68 as a safety measure to break the circuit 68 in the event of a continuous current ow therethrough.

To obtain the desired intermittent actuation of the magnet 24, a relay 78 is provided to open the normally closed switch 70. A circuit 80 controls the action of the relay 78, said circuit comprising a rectier 82 in series with a variable resistance 84 which communicates with one side of the VrelayV 78. A condenser 86 is arranged in parallel relationship with the relay 78.

When power is supplied to the circuit 68, the normally closed switch'7t will remain closed for a small interval of time until the condenser 86 reaches a fixed percentage of the maximum applied voltage. This is conventionally known as the standard time constant and is due to the presence of a resistance in the circuit. After the voltage builds up to pull in voltage, the relay 78 is energized which opens'tlie switch 70 and breaks the circuit to the magnetv 24. TheV condenser 86 begins to discharge through the relay 78 holding the switch 70 open for a fixed period of time. Upon discharge of the condenser 86 the normally closed switch 70 will snap closed, reenergizing the magnet 24 and the above cycle will be repeated.

The variable resistance 84 provided in the circuit 80 is to accommodate variation in the line voltage which may'effect proper operation of the relay 78. It has been found desirable to hold the magnet on time to the minimum required to urge the plate 12 to its maximum downposition adjacent the bottom wall and to then immediately de-energize the Vmagnet so that the upward stroke may immediately be begun. This optimum performance is achieved by having a proper voltage at the relay 78. For example, if the line voltage is considerably lower than standard, the resistance 84 may be decreased which will bring the voltage to the relay 78 to the proper level'. In the alternative, if the' line voltage is excessive, the resistance 84 may be increasedV to again return the voltage to the relay 78 to the proper level. This feature is important in view of the fact that proper bath temperature control is partially dependent upon proper bath agitation, which in turn is responsive to the action of the plate 12, and the action of the plate 12, obviously, is determined by the proper timing of the intermittently energized magnet 24. n

'Directing attention to Figures 4 and 5, wherein is illust'rated the temperature controlling Switch unit 56. As earlier noted, the unit 56 comprises a pair of switches 58 and` 60, said switches being mounted on a carriage 90 which is pivotally supported on a pin 92. A conventional tempe'rature sensitive hydraulic diastat assembly 94 is secured to a ix'ed base plate 96 and is arranged tov operatively engage the frame 90 as at 98. The diastat 94 will move linearly, as seen in Figure 5, in response to temperature variation as sensed by the bulb 64, Vthe latter being conventionally connected to the diastat as is familiar to those skilled inthe art. Manual movement of a control knob will also induce the linear movement Vof the diastat. A tension spring 102 is provided and has its opposite ends connected to the lixed base plate 96 and pivotally movable carriage 90, respectively, whereby the carriage 90 is continually biased toward the fixed plate 976. Y u u An adjusting screw 104 may be threadably mounted asiais'a in the fixed plate 96 and arranged to extend inwardly to engage a spring arm 106 which is normally flexed away from an actuating button 108 of the switch 58. The adjusting screw 104 may be set in any desired position, whereby upon movement of the carriage 90 toward the xed plate 96 in response to a linear change of position of the diastat assembly 94, the spring 106 will abut the end of the screw 104 and be urged toward the button 108. Continued movement of this nature will close the switch and complete the circuit 48, providing, of course, that selector switch 62 is in proper position. This in turn will energize the circuit 52, providing power to the heating elements 34.

A lower set screw 110 is threadably mounted in the base plate 96 and is arranged to extend inwardly adjacent a spring arm 112, said spring arm 112 being normally flexed away from the actuating button 114 of the switch 60. Another spring arm 116 is positioned in horizontal alignment with the spring arm 112, said spring 116 having a base portion 120 which is engageable with the button 114 and is normally flexed toward said button to provide for the closing of the switch 60. The spring arm 116 is further provided with a hook portion 122 (Figure 4) which overlaps the end of the spring arm 112. Thus it will be seen that the arm 120 and the arm 112 are normally flexed in opposite directions and it will be understood that the arm 112 is provided with a stronger exing capacity than the arm 116, whereby the arm 112 normally holds the base portion 120 away from the button 114.

The adjusting screw 110 may be set in any `desired position, whereby upon movement of the carriage 90 toward the base plate 96 the end of the screw 110 will abut the spring arm 112 and force it toward the switch 60 thereby relieving the pressure of the spring arm 112 on the spring arm 116 whereby the latter, due to its normally exed action, will engage the button 114 and close the switch 60. Again this action will close the circuit 48 and provide power to the heating elements 34 as above described, provided that the selector switch 62 is in proper position. Thus it will be seen that either switch 58 or 60 may be used to control heat application through the heating elements 34.

In the operation of the embodiment of Figures l through 6, it will be understood that suitable liquid may be supplied to the compartment 4 in any conventional manner. A thermometer (not shown) may be positioned in the liquid in the bath and the main switch 42 closed to provide power to the entire arrangement. The manually operated control knob 100 is then placed in a control reference position. The switch 62 is placed in either position and the corresponding switch 53 or 60 is closed, via the associated adjusting screw, to complete the circuit 48 through the relay 46. This will cause the switch 50 to close and power will be supplied to the heating elements 34 to provide for initial run-up of the bath temperature. Concurrently with this action the magnet control circuit is also energized whereby the electromagnet 24, as above described, is periodically supplied with power to direct the plate 12 downwardly toward the bottom wall 8 of compartment 4. In view of the fact that the plate 12 is provided with a plurality of holes or apertures 121, preferably distributed throughout the entire surface of the plate, the downward motion of the plate in the liquid causes a gentle agitation of the liquid throughout the entire body thereof. The provi-sion of the plurality of holes 121 acts like a multiplicity of small pumps to force the liquid below the plate upwardly as the palte is moved down toward the wall 8. This downward movement stresses the leaf springs 14. It should be noted that the leaf springs 14 are highly llexible and are easily overcome by the pull of the magnet, whereby the `downward movement of the plate 12 is firm and positive. Upon opening of the switch 70, as above described, the leaf springs 14 gently urge the plate 12 upwardly. Ofl course, other arrangements such as pontoons or floats which would support the plate 12 could be secured thereto to accomplish the upward movement of the plate. Thus it will be seen that the arrangement provides circulation of the liquid within the bath and because of the physical arrangement of the plate 12 positive agitation of the entire bath is assured as shown by arrows 15.

As the bath approaches the desired temperature, the adjusting screw is reset until it is properly located so that slight horizontal movements of the diastat assembly 94, induced by liquid temperature changes sensed by the bulb 64 and translated into pivotal movement of the switch carriage 90, will `alternately open and close the related switch to apply heat to the liquid and thereby maintain the bath temperature at a substantially constant value. Once this setting achieved, I have found that my novel control arrangement will maintain bath temperature within a tolerance of plus and minus 1A" C. Variations from the selected temperature may be achieved through manual turning of the knob from the set reference point, such turning serving to mechanically reposition the diastat assembly.

Directing attention to Figures 7 and 8, wherein is shown a slightly modied embodiment of the invention, it will be seen that the bath herein comprises a base 130, said base having a cylindrical jar 132 mounted thereon which denes a liquid compartment 133. A heating element 134 extends downwardly into the jar and is peripherally disposed therearound at a point adjacent the bottom thereof. An electromagnet 136 is disposed in the base and has va core which extends upwardly through the bottom of the jar, asiat 138. A conventional sealing arrangement 140 is provided to prevent escape of the liquid in the bath. A bottom plate 142 is located in the lower portion of the jar and is substantially coextensive with the horizontal cross-sectional area of the jar. A pair of upstanding pins 144, 144 are secured to the plate 142.

A pump plate arrangement 146 is supported by the plate 142 and comprises a generally flat rigid base plate 148 centrally located in the jar 132 and occupying an area considerably less than the total cross-sectional area of the compartment 133. Directing attention to Figure 7, it will be seen that a weighted arm is provided in obtuse angular relation to the plate 148. A pair of apertures 152 are provided, said apertures receiving the guide pins. 144 to maintain the entire arrangement in proper location in the bath.

The electrical control arrangement of this embodiment is the same as that described for the previous embodiment in that the magnet 136 is periodically energized to urge the plate 148 downwardly toward the bottom 142 as shown in phantom at 156. As the plate 148 is firmly moved downwardly, the liquid thereunder is squeezed outwardly toward the sides of the jar 132 which sets up convection currents throughout the entire body of the liquid as indicated by arrows 145. When the plate 148 reaches the maximum downward position, as shown in phantom at 156, the weighted portion 150 is raised off the bottom 142 and eccentrically loads the plate 148. Upon the de-energizing of the magnet 136, the weighted portion 150 gently urges the plate portion 148 upwardly to its original position. Thus it will be seen that in this embodiment a gentle periodic pulsation is applied to the liquid in the bath to provide for uniform circulation of the liquid throughout the bath.

It will be understood that the embodiment of Figures 7 and 8 is particularly adaptable to relatively small bath arrangements. On the other hand, the embodiment of Figures l through 3 is usually employed in bath arrangements of medium sizes. Where a bath arrangement of relatively large size is desired, a plurality of plates, such as plate 12, and/ or controlling magnets may be provided throughout the area of the bath to assure proper agitation of the liquid in the bath.

Returning again to Figures 4 and 5, it will be seen that the novel controlling switch arrangement 56 provides an additional function that is particularly useful in many bath applications where two common bath temperatures are frequently and alternately used. As earlier noted, either switch 58 or 60 may be used to control the bath temperature. Where two temperatures are Vfrequently used the 'adjusting screw 104 may be so set, whereby switch 58 will control the lower of the two temperatures. The adjusting screw 110 may be selectively set whereby the switch 60 will control the higher of the two temperatures. Once these settings are accurately located, the bath operator need only change the setting on the selector switch 62 to change the temperature control from switch 58 to 60 or vice versa and thereby select either the higher or lower desired bath temperature. Temperature variation from either the high or the low controlling temperatures may again be made by manually turning the control knob 100. Y

A particular feature of the switch arrangement 56 that renders this multiple temperature selection possible is the physical arrangement of the spring arms 116 and 112. It will be remembered that the arm 116 will engage the button 114 when the pressure of the arm 112 thereagainst is relieved, by engagement of the latter by the screw 110. The spaced provision between the arm 112 and the base 120 of the arm 116 will allow continued biasing movement of the carriage 90 toward the plate 96 after engagement of the screw 110 with the arm 112. This overtravel allowance will enable the switch 58 and the associated spring arm 106 to be moved into operative engagement with the associated screw 104 when the switch 58 is controlling the circuit 4S to afford the selected low bath temperature.

Thus it will be seen that the invention provides a novel bath arrangement which solves the problems heretofore existent in the art and affords both accurate bath temperature control Vover extended periods of time and further provides a oath having an even temperature throughout at any given instant of time. The arrangement further provides a clear unobstructed working area and avoids any possibility of specimen container breakage andthe like due to contact between the liquid agitating means and said container. It will be understood that certain bath applications Vrequire the maintenance of a bath temperature considerably lower than the normal environmental temperature and that Vin suchV applications refrigerating or cooiing means may be substituted for the heating means disclosed. With this in mind the term heat control means as used herein will be understood to mean either heating or cooling arrangements that may be used to control bath temperature at any desired level.

The invention as herein disclosed may be subject to many variations without departing from the spirit thereof or the scope of the appended claims.

I claim:

l. In a liquid bath arrangement, a liquid containing compartment, a movable relatively non-flexible plate located in the compartment and normally submerged in the liquid therein, means to intermittently move said plate from a iirst position to a second position, said means being without direct mechanical connection to the plate, and other means to return said plate from said second position to said rst position whereby a gentle and uniform circulation of the liquid in the compartment is achieved.

2. A liquid bath arrangement according to claim l, wherein said plate comprises a magnetic attraction portion, and said rst mentioned means comprises an eiectromagnet, and control means to intermittently energize said magnet and create an intermittent magnetic held which attracts said portion and moves said plate to said second position.

3 A liquid bath arrangement according to claim 2, wherein said other means comprises spring means which are stressed in response to movement of the plate from said firstV position to said second position, whereby said spring means acts to return said plate to said first position when the electromagnet is de-energized.

4. A liquid bath arrangement according to claim 2, wherein said plate is mounted in said compartment for pivotal movement, and said other means comprises a balanceweight which eccentrically loads said plate in response to said pivotal movement from said rst position to said second position and thereby acts to return said plate when said electromagnet is de-energized.

5. In a liquid bath arrangement, a plurality of confining walls defining a compartment to store a body of liquid therein, heat control means associated with the arangement and responsive to the temperature of the liquid and operative to maintain said liquid at a predetermined temperature, and means to gently agitate the entire body of said liquid comprising at least one substantially rigid plate, said plate being carried in close adjacency to one of said walls leaving a substantial portion of said body of liquid without operating parts therein, and means operatively engaging the plate to induce reversible movement of the plate in the liquid and only in a limited portion of said compartment immediately adjacent said one wall.

6. A liquid bath arrangement according to claim 5, wherein the reversible movement is linear, and said plate is provided with a plurality of apertures scattered over the area thereof.

7. A liquid bath arrangement according to claim 5, wherein the reversible movement is pivotal.

8. A liquid bath arrangement according to claim 7, wherein the last mentioned means comprisesl a weight which is eccentrically positioned in response to movement of plate in one direction.

9. In a liquid bath arrangement, a liquid container compartment, heat control means in the compartment adjacent and in spaced relation to the bottom, control means for heat control means responsive to temperature variation of the liquid in the compartment, means to agitate the liquid in the compartment comprising substantially flat plate means positioned intermediate the heating means and the bottom, an electromagnet adjacent the bottom and below the plate, control means to alternately energize and de-energize the magnet whereby upon energizing of the magnet the plate is moved through the liquid toward the bottom, and means to move the plate away from the bottom and toward the heat control means upon de-energizing of said magnet.

l0.V A liquid bath arrangement according to claim 9, wherein said plate means is substantially coeXtensive with the horizontal cross-sectional area of said compartment, said plate means having a plurality of apertures disposed throughout the area thereof, and said last mentioned means comprises at least one leaf spring secured to the plate and engaging the bottom, said spring being stressed by movement of the plate toward the bottom whereby said spring will be operative to move said plate toward said heat control means.

ll. A liquid bath arrangement according to claim 9, wherein said plate is solid throughout its area and occupies substantially less than the entire cross-sectional area of the compartment, saidplate having one edge thereof pivotally engaging the bottom, and said last mentioned means comprises a weight secured to the plate and engaging the bottom when the plate is in raised position, said weight being elevated` as the plate is moved toward the bottom under the action of the magnet, whereby the weight will act to move the plate upwardly toward the heating means when the magnet is de-energized.

l2. A liquid bath arrangement according to claim 2l, wherein said carriage is pivotally movable, said biasing means comprising a sprin'J interconnecting the carriage and base biasing the carriage toward the base, said switch means comprising a pair of switches on the carriage, said abutment means comprising an adjusting screw asso- 9 ciated with each switch, and a selector switch device to selectably determine which switch of said pair will control said electrical circuit whereby different predetermined bath temperatures may be easily selected.

13. A liquid bath arrangement according to claim 12, and including a single spring arm associated with one switch and interposed between the one switch and the related adjusting screw, said arm being normally ilexed away from the switch, a pair of spring arms associated with the other switch and interposed between the related adjusting screw and said other switch, one of said pair of spring arms being normally exed away from the other switch, a breakable connection between said pair of spring arms whereby said other arm will hold said one arm away from the other switch, said other arm being engageable with the related adjusting screw to break said connection and allow said one spring arm to engage said other switch in response to movement of the carriage.

14. A control arrangement for a liquid bath of the type described comprising a linearly movable member movable in response to temperature change in the bath or upon manual adjustment thereof, a liXed base, a carriage pivotally mounted on the base and engageable with said member to be moved thereby, a tension spring interconnecting the b'ase and the carriage and biasing the latter toward said member, a pair of switches on the carriage, an adjusting screw threadably mounted in the base adjacent each switch, a flexible arm interposed between one switch and the related screw and normally biased away from the switch and toward the screw, a pair of flexible arms interposed between the other switch and the related adjusting screw, each arm of said pair being biased in opposite directions, a breakable connection between said pair of spring arms whereby both of said arms are held in spaced relation to said other switch, one of said spring arms being engageable with the related adjusting screw to break said connection and allow the other of said spring arms to engage the other switch, said spring arms being engageable with the related adjusting screw upon movement of the carriage toward the base.

15. A liquid bath arrangement according to claim 3, wherein said spring means comprise at least one leaf spring interposed between and operatively engaging the plate and the compartment.

16. In a liquid bath arrangement of the type described, a plurality of walls defining a liquid containing compartment, at least one of said walls being formed of nonmagnetic material, a liquid pump plate mounted for movement in the compartment and adjacent said one wall, an electromagnet carried by the arrangement adjacent said one wall and on a side thereof remote from the location of the plate, a magnetically responsive portion on said 1@ plate and in the compartment, and means to periodically energize said electromagnet to provide an intermittent magnetic field to magneticaly engage said portion and induce movement of said plate in one direction.

17. A liquid bath arrangement according to claim 16 and including means to move said plate in another direction upon de-energizing of said electromagnet.

18. A liquid bath arrangement according to claim 17, wherein said last mentioned means comprises leaf springs operatively interposed between the compartment and the plate, and guide means in the compartment to guide said plate during said movement.

19. A liquid bath arrangement according to claim 17, wherein said plate is mounted for arcuate movement in the compartment, and said last mentioned means comprising weight means to eccentrically load said plate upon movement thereof in said one direction.

20. A liquid bath arrangement according to claim 17, wherein said electromagnet is a direct current magnet, and said means to periodically energize said magnet comprises an electrical circuit through said electromagnet, rectifying means in series with said magnet, condensing means in parallel with said magnet, said circuit having a breakable switch in series arrangement with said rectifying means and said magnet, and means to periodically open said switch to accommodate deenergizing of said magnet.

21. In a liquid bath arrangement, a liquid container, electrical heating means to heat the liquid therein, and a control arrangement to determine the action of the heating means comprising a sensing device in the liquid to detect temperature change therein, a ixed base, a movable diastat assembly mounted on and movable relative to the base in response to temperature change noted by said sensing device, a movable carriage operatively engaged by the assembly to move therewith, switch means on and carried by the carriage, adjustable abutment means mounted on the base, biasing means to urge the carriage toward the abutment means resulting in operative engagement between the abutment means and the switch means, whereby said switch means are actuated and deactuated in response to movement of the carriage.

References Cited in the file of this patent UNITED STATES PATENTS 1,165,958 Freas Dec. 28, 1915 1,397,766 Lidberg Nov. 22, 1921 1,411,417 Croy et al. Apr. 4, 1922 1,776,405 Wilsey Sept. 23, 1930 2,513,577 Malme July 4, 1950 2,543,818 Wilcox Mar. 6, 1951 

